1. Technical Field
The present invention relates to aircraft. In particular, it relates to aircraft with wings capable of simultaneous movement along two axis, including a sliding motion on a first axis and a rotating motion on a second axis.
2. Background Art
A variety of aircraft types are currently in wide use. For example, heavy fixed wing aircraft, ultralite aircraft, and hang gliders. While substantially different in many respects, each of these aircraft types share wing structures which are fixed or able to move about one axis only.
The development of hang gliders has provided flyers with a relatively inexpensive and easy method of flying. Hang gliders currently in general use are based on the standard Rogallo type glider. Rogallo type hang gliders are typically constructed with leading edges arranged to intersect a keel at a forward point. The leading edges are connected by a cross bar and a control bar is suspended from the cross bar. A sailcloth is stretched over the leading edges and battens to form a fixed type wing. Flight is accomplished by catching an updraft and are controlled by shifting the pilot's body weight on the control bar. Some hang gliders have been developed which are designed to allow the pilot to flap the wings about a single fixed vertical axis to assist lift. These structures all result in a limited amount of control over wing motion which in turn reduces safety and performance.
While hang gliders typically have flexible wings, heavy aircraft have rigid wings which usually are made from metal. While most heavy aircraft have fixed wings, there are some high performance military aircraft as well as supersonic commercial transport aircraft which allow the wings to pivot about a single fixed horizontal axis. The wing movement is designed to increase lift during takeoff by extending the wings to a position which is relatively perpendicular to the fuselage, and to decrease drag and increase performance by sweeping the wings back during high speed flight.
Utralites exhibit characteristics of the hang glider and heavy aircraft. The wing structures in this type of aircraft are typically fixed and share the same safety and performance drawbacks exhibited by hang gliders and heavy aircraft. It would be desirable to have a wing structure for any of the foregoing aircraft types which would provide greater control, safety and performance characteristics.
Another problem associated with hang gliders is the difficulty associated with becoming airborne. While hang gliders with a variety of wing shapes have been developed, each of them has a wing fixed to a keel. With such hang gliders, the pilot is required to make an approach run so as to catch an updraft or to leap down from a high place. Therefore, it is necessary to find a location with a difference in altitude between the taking off point and the landing point, and even if the take off by way of an approach run is successful, it is difficult to soar continuously for many hours unless an updraft is caught properly by the wing. In flat areas, the only way to launch a hang glider is through outside assistance, such as being towed aloft by a powered aircraft in the same manner as a conventional glider. Power assisted takeoff is usable from the origin point of the flight. However, once the hang glider has landed away from the airfield which provided the towing, power assisted takeoff for return trips would not be available. As a result, hang gliders require locations with physical areas that are suitable for relaunching in order to return. In flat areas, this may not be possible. Therefore, it would be desirable to have an easy method of relaunching a hang glider from a flat surface.
Hang gliders have been developed with wheeled frames which form an enclosure for supporting a person suspended from the neutral point of the wing. The pilot is seated in the enclosure which may have an internal combustion engine fixed behind the user. The powered hang gliders of this type provide extended flying time, but there are also several drawbacks associated with this type of aircraft. One disadvantage is that the motorized enclosure is heavy, bulky, and difficult to transport. This detracts from the ease of transport associated with conventional hang gliders. The weight of the enclosure is also a serious functional drawback since it requires the motor to operate continuously to keep flying. If the motor stops, the sink rate is high. In addition, such enclosures are usually bare frames without any kind of streamlining. Therefore, another functional drawback is the high aerodynamic drag associated with this design. Attempts to overcome these disadvantages, such as increasing the wing area and/or the motor power of the aircraft have been made. However, as the wing span increases and/or the power increases, the motorized hang glider ceases to be a very light and maneuverable aircraft suitable for gliding sport and tends to become more like an ultralite. It would be desirable to provide an enclosure which did not have the increased drag of prior art devices.
Other means have also been devised to motorize a hang glider without resorting to a wheeled enclosure. For example the motor and prop may be fixed under the keel of the wing in one of two positions relative to the center of gravity: a first position in which the motor is behind the center of gravity with the propeller in front, which is referred to as a puller system; and a second position in which the motor is in front of the center or gravity with the propeller behind, which is referred to as a pusher system. These solutions improve upon the weight and drag penalties created by the hanging enclosure. In particular, the pilot can be in a prone position hanging from the wing by means of a harness which results in reduced drag.
Unfortunately, mounting the power unit on the keel of the wing gives rise to piloting difficulties which may be dangerous since by definition a hang glider is controlled in flight by the pilot's movements relative to the wing's center of lift. The weight of the fixed motor reduces the effect of the pilot's movements and therefore reduces the pilot's control of the aircraft in flight. It would be desirable to have the advantage of powered flight without the disadvantages associated with the additional weight that causes loss of control.
A third system consists in strapping the motor to the pilot's back. The combined pilot and motor weight increases the effects of pilot body movement on aircraft control, but substantially adds to the danger in the event of a crash. Also, the drag is substantially increased because the pilot must remain in an upright position during flight. Another difficulty stems from the fact that take off is possible only from a suitable slope. Further, motorized take off is also physically difficult, except in the case of the wheeled enclosure, but in that case the drag and the weight of the enclosure reduces the performance of the motorized hang glider once airborne.
The ultralite and heavy aircraft exhibit similar drawbacks. In particular, the maximum performance characteristics cannot be achieved because the wings are either fixed or restricted in motion.
Another disadvantage of prior art hang gliders is the need to manually control the wings. This results in pilot fatigue and reduces the amount of time which the pilot can comfortably fly. It would be desirable to control the hang glider wing with a power assist that would not tire the pilot.
The prior art has failed to provide a method of controlling wing position to increase safety be increasing pilot control and to maximize takeoff and flight performance which allows the wing to move on more than one axis. The prior art has failed to provide an easy method of taking off hang gliders from flat surfaces. Further, the prior art has not provided a convenient method of assisting takeoff from flat surfaces which does not involve powered units.